Exterior doors of an aircraft are essential elements of the aircraft and need to fulfill certain safety requirements. For instance after landing an aircraft, a residual pressure may be present in a cabin of the aircraft, i.e. the air pressure in the cabin might be higher than an atmospheric pressure in an environment of the aircraft, and the door may not be opened before such pressure difference has dropped to a certain harmless level. Moreover, aircraft exterior doors are usually equipped with emergency or evacuation slides serving to evacuate passengers and cabin crew in case of an emergency landing.
As exterior doors of aircrafts are usually operated and actuated manually by a cabin attendant after landing, they are nowadays equipped with warning systems triggering a visual and/or acoustic warning signal in case a door is supposed to remain closed and/or locked. Such warning signals may be triggered if a residual pressure is present in the cabin or if a door is actuated while an emergency slide of the respective door is still armed.
WO 2006/077111 A1 and DE 10 2005 002 544 A1 disclose a pressure difference warning system comprising a pressure sensor for measuring a pressure difference between an interior and an exterior region of an aircraft. The warning system further comprises an acoustic signal device designed for outputting an acoustic signal if a measured pressure difference exceeds a specifiable threshold value.
WO 2013/160390 A2 and DE 10 2012 206 877 A1 describe a device for a cabin pressure difference warning for an aircraft or spacecraft comprising a cabin pressure difference sensor means and contact sensor means for detecting a contact by a user with an operating element. The device further comprises a warning signal emitting means for emitting a pressure difference warning signal.